In this study, an attempt was made to develop a new simplified groundwater vulnerability to contamination index (SGVI). Nine experts in the fields of groundwater, surface water, soil, landuse and GIS were interviewed to develop the new index. They were asked to agree on new parameters that could be used to investigate groundwater vulnerability. Data about such parameters must be affordable and inexpensive. Subsurface parameters were excluded due to the fact that most researchers might not have adequate data about them. The experts agreed that depth to groundwater, soil texture, lineament density, rainfall, topographic slope, drainage density and landuse/land cover parameters should be included in the new vulnerability index. The experts were also asked to give a weight and the ratings for each parameter. The weights given by the experts were subjected to AHP analysis to determine the exact weight for each parameter. An area of 3200 km 2 in the northern part of Jordan was selected to test the SGVI. The final map of the SGVI showed that most of the area (more than 96%) had moderate-low and moderate-high vulnerability to contamination. The new index was also subjected to statistical analysis, map removal test and map removal sensitivity analysis. The outcomes of these analyses showed that the new index was applicable and could be used in areas where subsurface data was limited or not available.
The maps of Groundwater vulnerability to contamination are important tools used to assist the landuse planners in addressing the problems that groundwater might have as a result of changing the landuse in a certain area. It is also used to predict the pollutants movement in the soil. This will allow planners to modify the potential harm to groundwater before serious impacts occur [
There are several methods used to assess the groundwater vulnerability inclu- ding process-based mathematical models, statistical methods and overlay and in- dexing.
The process-based mathematical models are analytical or numerical solutions of mathematical equations to predict the contaminant transport in both space and time, which distinguish them from the other methods. These methods are constrained by the lack of data and the computational difficulties [
The statistical models are usually used in evaluating, determining, and quanti- fying the association between measures of vulnerability and various types of information that could be related to vulnerability. The use of statistical methods is limited by the requirement for high quality data, cost and time constrains [
The overlay and index methods are used for combining maps of parameters considered to be important in contaminant, where each attribute is assigned a numerical score based on its perceived importance [
Examples of the developed overlay and index methods include the following (
1. DRASTIC ( [
2. GOD ( [
3. EPIK ( [
4. SINTACS ( [
5. PI ( [
6. COP ( [
It appears from
Parameters | Methods | |||||
---|---|---|---|---|---|---|
GOD | DRASTIC | SINTACS | EPIK | PI | COP | |
Topographic slope | a | a | a | a | a | |
Stream network | a | a | a | |||
Soil | a | a | a | a | a | |
Net recharge | a | a | a | a | a | |
Unsaturated zone | a | a | a | a | a | a |
Depth to water | a | a | a | a | ||
Hydrogeological features | a | a | a | a | a | |
Aquifer hydraulic conductivity | a | a | ||||
Aquifer thickness | a | |||||
Land use | a | a | a | a |
the unsaturated zone (GOD, DRASTIC, SINTACS, EPIK, PI and COP), hydraulic conductivity (DRASTIC and SINTACS) and aquifer thickness (SINTACS). Also, these methods require data about net recharge (DRASTIC, SINTACS, EPIK, PI and COP). These data requirement might restrict researchers and lead them either to estimate or exclude one or more of these parameters. [
This research is an attempt to derive a Simplified Groundwater Vulnerability Index (SGVI) based on experts’ opinions using available and inexpensive data to assist researchers in assessing groundwater vulnerability as a part of their Environmental Impact Assessment (EIA).
The adopted methodology for developing a simplified groundwater vulnerability index (SGVI) was based on the Analytical Hierarchy Process (AHP). AHP is ba- sed upon the construction of a series of Pair-Wise Comparison Matrices (PCMs), which compare each criterion to one another. The scale of PWC is divided from 1 to 9 for PCM elements to estimates the relationship between the criteria on the scale (9, 7, 5, 3, 1) where the value of 1 suggests that the criteria are equally important and a value of 9 leads one to infer that the criterion under consideration is extremely important in relation to the other criterion with which the compa- rison is made [
The processes of pairwise comparison matrix that are computed to achieve and check the pairwise comparison matrix is acceptable or not are illustrated in
Based on [
λ represents the sum of consistency vectors divided by number of the consistency vector.
Where A is the known judgment matrix and n is the order of the matrix B.
Intensity of importance | Definition | Intensity of importance | Definition |
---|---|---|---|
1 | Equal importance | 6 | Strong to very strong importance |
2 | Equal to moderate importance | 7 | Very strong importance |
3 | Moderate importance | 8 | Very to extremely strong |
4 | Moderate to strong importance | 9 | Extreme importance |
5 | Strong importance |
CI represents the consistency index based on the observations of λ.
Where λmax is the average value of the consistency vector, and n is the number of criteria.
The consistency Ratio (RI) is calculated using Equation (3):
In this research, nine experts from various Jordanian universities and organisations in the fields of groundwater, surface water, soil, landuse and GIS were interviewed to suggest a Simplified Groundwater Vulnerability Index (SGVI) that requires inexpensive data. The experts agreed that the following parameters should be included in the groundwater vulnerability index:
Depth of Groundwater (DG): Depth determines the depth which a contaminant must travel before reaching the aquifer.
Soil Texture (ST): Soil has a significant impact on the amount of recharge water which infiltrates into the groundwater.
Lineament Density (LD): Higher values of lineament density might pose more threat to groundwater by allowing contamination to reach the water table.
Rainfall (RF): Rainfall is the major carrier of contamination to groundwater through infiltration.
Topographic Slope (TS): Slope controls the likelihood that a pollutant will run off or remain on the surface long enough to infiltrate.
Drainage Density (DD): Drainage density is a useful measure for runoff potential. High drainage density means higher potential for runoff and hence less infiltration.
Land Use/Land Cover (LL): Landuse/Land cover affect the potential for groundwater recharge and hence impact the groundwater vulnerability to contamination.
The experts were also asked to put a weight to each parameter based on the supplied simple questionnaire listed in
matrix of the experts opinions was then calculated (
N | RI | N | RI | N | RI | N | RI | N | RI |
---|---|---|---|---|---|---|---|---|---|
1 | 0.0 | 4 | 0.90 | 7 | 1.32 | 10 | 1.49 | 13 | 1.56 |
2 | 0.0 | 5 | 1.12 | 8 | 1.41 | 11 | 1.51 | 14 | 1.57 |
3 | 0.58 | 6 | 1.24 | 9 | 1.45 | 12 | 1.54 | 15 | 1.59 |
More importance | Equal importance | Less importance | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Parameters | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | Parameters |
DG | DG | |||||||||||||||||
ST | ST | |||||||||||||||||
LD | LD | |||||||||||||||||
RF | RF | |||||||||||||||||
TS | TS | |||||||||||||||||
DD | DD | |||||||||||||||||
LL | LL |
also asked to suggest the ratings for each parameter based a scale 1 (Lowest) to 4 (Highest).
In order to test the SGVI, an area in the Northern part of Jordan was selected as shown in
The investigated has an area of 3200 km2 which comprises 3.59% of the total area of Jordan. The climate within the investigated area is characterised by hot dry summers and wet cold winters. Rainfall varies between 50 mm in the South East to 150 mm in the North West (
Elevation in the area varies between 530 m above sea level in the South and South East to 1224 m above sea level in the North near the Syrian border (
Surface water flows from the North towards the South and South West. Most of the Drainages is coming from Syria and flow towards the Azraq Oasis to the South of the investigated area (
The soil texture within the investigated area is classified into 4 classes: Loam, Sandy Loam, Silt Loam and Silty Clay Loam as shown in
more than 300 m in the North. This variation is due to the high variation in ground topography that characterise the area.
Criteria | DG | ST | LD | RF | TS | DD | LL |
---|---|---|---|---|---|---|---|
DG | 1 | 2 | 2 | 2 | 2 | 2 | 2 |
ST | 0.5 | 1 | 1 | 2 | 2 | 2 | 2 |
LD | 0.5 | 1 | 1 | 1 | 2 | 2 | 2 |
RF | 0.5 | 0.5 | 1 | 1 | 1 | 2 | 2 |
TS | 0.5 | 0.5 | 0.5 | 1 | 1 | 1 | 1 |
DD | 0.5 | 0.5 | 0.5 | 0.5 | 1 | 1 | 1 |
LL | 0.5 | 0.5 | 0.5 | 0.5 | 1 | 1 | 1 |
Sum | 4 | 6 | 6.5 | 8 | 10 | 11 | 11 |
Parameters | DG | ST | LD | RF | TS | DD | LL |
---|---|---|---|---|---|---|---|
Weights (priority vector) | 0.244 | 0.18 | 0.162 | 0.136 | 0.099 | 0.09 | 0.09 |
λmax | 8.071 | ||||||
CI | 0.179 | ||||||
RI | 1.32 | ||||||
CR | 0.1 |
Parameters | Weight | Ratings | |||
---|---|---|---|---|---|
1 | 2 | 3 | 4 | ||
DD (m) | 0.244 | >150 | 100 - 150 | 50 - 100 | 0 - 50 |
ST | 0.18 | Loam | Silt Clay Loam | Silt Loam | Sandy Loam |
LD (km/km2) | 0.162 | 0 - 1.5 | 1.5 - 2.5 | 2.5 - 3.5 | >3.5 |
RF (mm) | 0.136 | <50 | 50 - 100 | 100 - 300 | >300 |
TS (%) | 0.099 | >8 | 4 - 8 | 2 - 4 | 0 - 2 |
DD (km/km2) | 0.09 | >2.25 | 1.5 - 2.25 | 0.75 - 1.5 | 0 - 0.75 |
LL (Class) | 0.09 | Bare Rock and Urban | Bare Soil | Marab | Agricultural and natural vegetation |
Class | No Risk | Low | Moderate-Low | Moderate-High | High | Very High |
---|---|---|---|---|---|---|
Range | 1 - 1.5 | 1.5 - 2 | 2 - 2.5 | 2.5 - 3 | 3 - 3.5 | 3.5 - 4 |
The data needed for this research were collected at no cost from various resources within Jordan and from internet resources.
The following flowchart (
The soil texture map shown in
The density function in ArcGIS was used to calculate the lineament density for the investigated area, which then classified according to
The rainfall isohyets map shown in
The slope map for the investigated area was extracted from the ASTER DEM (30 m) for the investigated area (
ASTER DEM was used to generate the drainage map for the investigated area (
Data Type | Source |
---|---|
Depth to Groundwater | Water Authority of Jordan (Excel format) |
Soil Texture | Jordan Ministry of Agriculture (1:250,000) |
Lineament | Natural Resources Authority based on Landat ETM (30 m) |
Rainfall | Department of Meteorology (Excel format) |
Topographic Slope | ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) DEM (30 m) |
Drainage | Extracted from the ASTER DEM using Flow Direction and Flow Accumulation tools |
Landuse/Land Cover | Extracted from Landsat 8 imagery (30 m) of August, 2016 |
investigated area, which then classified according to
Landsat 8 imagery (30 m) of August 2016 was used to generate the landu- se/land cover map for the investigated area using unsupervised classification technique. The resulted map was subjected to GIS manipulation by adding the appropriate ratings according to
The final SGVI map (
The statistical analysis for the SGVI parameters (
contribute moderate risk of contamination with mean values of 0.244, 0.298, 0.269, 0.277 and 0.277 respectively.
The ST parameter is highly variable as its coefficient of variation (CV) value is
Class | Area (km2) | % of total area |
---|---|---|
No Risk | 6.58 | 0.2 |
Low | 1161.42 | 36.3 |
Moderate-Low | 1929.70 | 60.3 |
Moderate-High | 102.30 | 3.2 |
Total | 3200 | 100 |
DG | ST | LD | RF | TS | DD | LL | |
---|---|---|---|---|---|---|---|
Min | 0.244 | 0.18 | 0.162 | 0.136 | 0.098 | 0.09 | 0.09 |
Max | 0.244 | 0.72 | 0.648 | 0.408 | 0.392 | 0.36 | 0.36 |
Mean | 0.244 | 0.384 | 0.298 | 0.269 | 0.277 | 0.255 | 0.358 |
SD | 0 | 0.192 | 0.113 | 0.057 | 0.091 | 0.05 | 0.025 |
CV(%) | 0.00 | 50.00 | 37.92 | 21.19 | 32.85 | 19.61 | 6.98 |
50%. The DG parameter has no variation within the investigated area as it has only a single value for the entire area (0.244). LD, TS, RF and DD are moderately variable with CV values 37.92% and 32%, 21.19% and 19.61% respectively. The LL co- ver parameter is the least variable parameter (CV = 6.98%). The sensitivity is calculated based on the rating and weights designated to the feature classes of each parameter.
The statistics on the removal of one statistically significant parameter on the SGVI values (
Map removal sensitivity analysis is a test developed by [
With: S is the sensitivity index of the parameter.
V is the intrinsic vulnerability index of the method; N is the total number of parameters used to calculate V; Vxi represents the intrinsic vulnerability index obtained after removal of the parameter X.
Based on the determined partial indexes (
Based on experts’ opinions, a new simplified groundwater vulnerability index was developed to investigate groundwater vulnerability to contamination. Seven parameters including depth to groundwater, soil texture, lineament density, rainfall, topographic slope, drainage density, and landuse/land cover were suggested by the experts. The common factor between these parameters is inexpensive data sources to build each one of them. This is in contradiction to the parame- ters found in other groundwater vulnerability indexes such as GOD, DRASTIC, SINTACS, EPIK, PI and COP.
Based on the outcomes of this research and the statistical tests conducted on the SGVI parameters, it is established that:
Soil texture and landuse/land cover contribute the highest risk of contamina-
Parameter Removed | Mean | Min | Max | SD |
---|---|---|---|---|
DG | 1.84 | 0.983 | 2.666 | 0.226 |
ST | 1.701 | 1.047 | 2.28 | 0.156 |
LD | 1.786 | 1.065 | 2.352 | 0.217 |
RF | 1.815 | 0.966 | 2.638 | 0.227 |
TS | 1.807 | 1.128 | 2.514 | 0.208 |
DD | 1.829 | 1.047 | 2.64 | 0.225 |
LL | 1.726 | 1.001 | 2.55 | 0.225 |
Parameters | Sensitivity Index | |||
---|---|---|---|---|
S Minimum | S Average | S Maximum | Standard Deviation (SD) | |
DG | 0.000 | 0.009 | 0.029 | 0.005 |
ST | 0.134 | 0.234 | 0.313 | 0.023 |
LD | 0.148 | 0.248 | 0.332 | 0.032 |
RF | 0.130 | 0.253 | 0.370 | 0.033 |
TS | 0.152 | 0.252 | 0.357 | 0.030 |
DD | 0.145 | 0.255 | 0.371 | 0.032 |
LL | 0.134 | 0.238 | 0.356 | 0.032 |
tion to groundwater while depth to groundwater, lineament density, rainfall, topographic slope and drainage density contribute moderate risk of contami- nation.
Depth to groundwater, drainage density, rainfall and topographic slope have the highest importance in the index.
All parameters have strong impacts on the index except the depth to ground- water.
Based on that, it is concluded that the new simplified groundwater vulnerability index (SGVI) is applicable to investigate groundwater vulnerability to conta- mination in areas where subsurface data is limited or not available.
Based on this conclusion, it is recommended to test the SGVI in combination with other indexes such DRASTIC, SINTACS or EPIK especially in areas where data for these indexes are available to compare its outcomes with their outcomes. It is also recommended to look for other parameters that might contribute to groundwater vulnerability to contamination under the condition which these parameters are affordable and inexpensive.
The authors of this research would like to acknowledge and appreciate the contribution of the Jordanian experts who assisted the research team in the development of the SGVI index.
Al-Adamat, R. and Al-Shabeeb, A.A.-R. (2017) A Simplified Method for the Assessment of Groundwater Vulnerability to Contamination. Journal of Water Resource and Protection, 9, 305- 321. https://doi.org/10.4236/jwarp.2017.93020